It is common in the production of hot mix asphalt to sample the finished product and analyze its composition for quality control purposes. Samples may be taken for analysis to insure that the proper proportions of aggregate materials of various particle sizes, as well as the proper combination of aggregate materials and asphalt binder, are being incorporated into the finished product. Such sampling and analysis is useful and necessary, but it has not been employed in such a way as to provide information that may be used to make real-time adjustments to the operation of the various components of the plant. Indeed, such sampling and analysis as is conventionally practiced may not indicate a problem in the mix design or other parameters until the asphalt product has been delivered to a job site and used. In addition, much of the sampling of the asphalt product (or its constituent components) is carried out by hand, and therefore, may not be representative of the asphalt product being produced. Furthermore, during rainfall and other adverse weather conditions, or when recycled asphalt binder-containing materials are included in the aggregate materials, it may be difficult to analyze the particle sizes of aggregate materials used in the production of asphalt to insure that the proper proportions of the various aggregate materials are being employed.
The surface temperature of hot mix asphalt may be as high as 250–350° F., which makes hand sampling at least uncomfortable and potentially dangerous. Furthermore, a worker who is charged with the responsibility of obtaining a hand sample from a hot mix asphalt truck will not likely be willing and may not be able to spend the time to take sample portions from various locations on the load in the truck bed to insure that he gets a representative sample. Nevertheless, the standard practice for sampling hot mix asphalt from truck transports is to take several portions of a sample from each truck using a flat-bottom scoop or a square-nose shovel. ASTM Designation D 979-96 specifies that at least three approximately equal increments should be taken from each truck load of asphalt sampled. Various state highway departments impose additional requirements on the sampler of asphalt, in an effort to insure that representative samples are obtained. For example, the Georgia Department of Transportation Sampling Procedure GSP-15 specifies that hand samples may be taken only after the “cone” of material in the bed of the truck is first shoveled off to a depth such that the resulting flat area is at least 60% as wide as the truck and at least six inches deep. Wyoming Department of Transportation Sampling Procedure 830.0 requires that for smaller trucks, a sample area must be prepared by removing the top 2–4 inches from each quarter of the load, while for larger trucks, at least two transverse trenches must be excavated across the load in the truck bed. The sample is then removed by pushing the shovel into each cleared area or trench at a 45° angle. Illinois Department of Transportation Sampling Procedure 4.7.1 requires that an equal amount of material is to be taken from locations approximately one foot below the top of each pile in the truck bed, at quarter points around the pile's circumference. Mississippi Department of Transportation Field Testing Procedure TMD-11-77-00-000 requires that at least three samples be taken from specified locations in the truck after first removing the top 2–3 inches of material at each sample point. All of these procedures require that the sampler work for a significant period of time in the bed of the truck atop the load of hot mix asphalt (or adjacent the truck bed from a sampling stand). Complying with such procedures is uncomfortable and may be dangerous, which makes proper sampling problematic.
It is known to use heating devices to facilitate the sampling and analysis of asphalt products. By heating the product to a level sufficient to burn off the volatile asphalt binder, the heating devices effectively isolate the aggregate materials contained in the product for more accurate sampling and analysis of the aggregate material distribution. Examples of such prior art heating devices are contained in U.S. Pat. No. 4,276,093 of Pickermann, U.S. Pat. No. 5,081,046 of Schneider, U.S. Pat. No. 6,000,935 of Regimand, et al. and U.S. Pat. No. 6,054,323 of Troxler. Other asphalt heating devices include rotating and/or tilting containers in which the asphalt may be heated. Such devices are described in U.S. Pat. No. 5,785,516 of Tanaka and U.S. Pat. No. 5,947,720 of Kelly. None of the devices described in these prior art patents, however, is part of an asphalt production plant having items of equipment that may be controlled on a real-time basis as the asphalt product is being produced.
It is also known that the particle size distribution in a quantity of aggregate materials may be determined more-or-less automatically. Thus, for example, U.S. Pat. No. 3,439,800 of Tonjes, U.S. Pat. No. 5,059,310 of Fischer et al. and U.S. Pat. No. 5,222,605 of Pogue describe methods and devices for automatically determining the proportionate amounts of various particle sizes of such a product. Such methods and devices, however, do not contemplate control of equipment such as is employed in the production of asphalt.
It would be desirable if an asphalt production plant could be developed having items of equipment that may be controlled on the basis of information about the quality and composition of the asphalt product and its various components that is obtained as the product is being produced. It would also be desirable if such a plant could be provided in which information about asphalt mix design and the gradation of the aggregate materials used in producing an asphalt product may be obtained at various stages of production and used to control the operation of various items of equipment.